The present invention relates to an optical/electrical hybrid substrate and more particularly to an optical/electrical hybrid substrate including an optical waveguide provided on a wiring board and serving to transmit a light signal between a light emitting device and a light receiving device.
In recent years, with an increase in a speed of an information communication, a light converted into an electric signal is used as a medium for the information communication. In the light communication field, it is necessary to convert a light signal into an electric signal or to convert the electric signal to the light signal, and to carry out various processings such as a modulation for a light in the light communication. For this reason, there has been developed an optical/electrical hybrid substrate over which the conversion processing is carried out.
FIG. 1 is a sectional view showing a conventional optical/electrical hybrid substrate.
As shown in FIG. 1, a conventional optical/electrical hybrid substrate 200 has a wiring board 201, an optical waveguide 202, vias 204 and 205, wirings 207, 208, 211 and 212, a solder resist 214, a light emitting device 216, and a light receiving device 217.
The wiring board 201 has a substrate body 221, through vias 222 and 223, upper wirings 225 and 226, lower wirings 228 and 229, a solder resist 232, and external connecting terminals 233 and 234.
The through vias 222 and 223 are provided to penetrate through the substrate body 221. The through via 222 has an upper end connected to the upper wiring 225 and a lower end connected electrically to the lower wiring 228. The through via 223 has an upper end connected to the upper wiring 226 and a lower end connected electrically to the lower wiring 229.
The upper wirings 225 and 226 are provided on an upper surface 221A of the substrate body 221. The lower wirings 228 and 229 are provided on a lower surface 221B of the substrate body 221. The solder resist 232 has an opening portion 232A for exposing a part of a lower surface of the lower wiring 228 and an opening portion 232B for exposing apart of a lower surface of the lower wiring 229. The external connecting terminal 233 is provided on the lower wiring 228 in an exposed portion to the opening portion 232A. The external connecting terminal 234 is provided on the lower wiring 229 in an exposed portion to the opening portion 232B.
The optical waveguide 202 is bonded onto the wiring board 201 with an adhesive 250. The optical waveguide 202 has a structure in which a clad layer 236, a core portion 237 and a clad layer 238 are laminated, and has V grooves 241 and 242, through holes 244 and 245, and mirrors 2470 and 2480. The V grooves 241 and 242 are formed on the clad layer 236, the core portion 237 and the clad layer 238. The V groove 241 has an inclined surface 241A in an inclination angle of 45 degrees. The V groove 242 has an inclined surface 242A in an inclination angle of 45 degrees. The through holes 244 and 245 are formed to penetrate through the clad layer 236, the core portion 237 and the clad layer 238. The mirror 2470 is provided on the inclined surface 241A. The mirror 2480 is provided on the inclined surface 242A.
The via 204 is provided on the through hole 244. A lower end of the via 204 is electrically connected to the upper wiring 225. The via 205 is provided on the through hole 245. A lower end of the via 205 is electrically connected to the upper wiring 226.
The wirings 207, 208, 211 and 212 are provided on the clad layer 238. The wiring 207 is electrically connected to the via 204 and the light emitting device 216. The wiring 208 is electrically connected to the light emitting device 216. The wiring 211 is electrically connected to the via 205 and the light receiving device 217. The wiring 212 is electrically connected to the light receiving device 217.
The solder resist 214 is provided to cover an upper surface of the clad layer 238 and a part of each of the wirings 207, 208, 211 and 212. The solder resist 214 has an opening portion 214A for exposing a part of an upper surface of the wiring 207, an opening portion 214B for exposing a part of an upper surface of the wiring 208, an opening portion 214C for exposing a part of an upper surface of the wiring 211, an opening portion 214D for exposing a part of an upper surface of the wiring 212, an opening portion 214E for causing a light signal of the light emitting device 216 to pass therethrough, and an opening portion 214F for causing the light signal to reach the light receiving device 217.
The light emitting device 216 is flip-chip connected to the wirings 207 and 208. The light emitting device 216 has the light emitting portion 247 for irradiating a light signal. The light emitting portion 247 is disposed opposite to the opening portion 214E. The light receiving device 217 is flip-chip connected to the wirings 211 and 212. The light receiving device 217 has the light receiving portion 248 for receiving the light signal. The light receiving portion 248 is disposed opposite to the opening portion 214F (for example, see Patent Document 1).    [Patent Document 1] JP-A-2000-304953
In the conventional optical/electrical hybrid substrate 200, however, the wirings 207, 208, 211 and 212 to be connected to the light emitting device 216 or the light receiving device 217 are provided on the clad layer 238. For this reason, there is a problem in that a size in a vertical direction of the optical/electrical hybrid substrate 200 is increased.
Moreover, the wirings 207, 208, 211 and 212 are provided on the clad layer 238. Therefore, it is necessary to provide the solder resist 214 for protecting the wirings 207, 208, 211 and 212 other than the portions to which the light emitting device 216 and the light receiving device 217 are connected. Consequently, there is a problem in that a cost of the optical/electrical hybrid substrate 200 is increased.